The present invention relates to a vehicle brake system which produces braking force automatically under predetermined conditions.
When the driver of a vehicle wishes to stop on a sloping road, or when the driver must stop the vehicle frequently on a congested road, it is desirable that braking force is produced while the brake pedal is not being depressed.
A vehicle brake system which produces braking force automatically under specific conditions is already known. In a well known power multiplier in which a shell body displaceably receives through a diaphragm a power piston which faces negative pressure applied to a front side constant pressure chamber and atmospheric air pressure applied to a rear side operation pressure chamber, the pressure difference produces thrust to the power piston which transmits the thrust to the output shaft. A manual brake switch is connected to a change over valve which is connected with the operation pressure chamber. By operation of the manual brake switch, the position of the change-over switch is controlled such that atmospheric air is introduced in the operation pressure chamber to automatically produce braking force. When vehicle speed decreases to a predetermined value, braking force is decreased.
When such known vehicle brake system operates on a downward slope, braking force is automatically produced. However, the braking force produced for a flat road is not sufficient for a downward slope, so that a vehicle which has slowed down may accelerate once more when braking force is decreased at a low speed.
The object of the present invention is to provide a vehicle brake system in which substantially similar deceleration is applied to the vehicle by automatically varying braking force on upward and downward slopes.